Parts per million (ppm) represents the ratio of a particular mineral in a nutrient solution. A ppm of 1 means that there is 1 millionth of a gram of that mineral for every gram of solution. Parts-per-million levels are used to control the optimal ratios of nutrients in fertilizer and other nutrient supplements. Very good pH tri-meters are available at hydroponic stores that give you a constant pH, ppm and temperature reading of your reservoir. Read more about ppm on Wikipedia.

Checking ppm levels or electrical conductivity (EC) is essential. If these measurements are too low, the plant will starve. If they are too high, the plant is put at risk of “burning” and may die due to oversalination and shock. It is very hard for plants to recover from overfeeding.

If your EC or ppm is too high, your plants will have nutrient burn and thus it is important to measure those values and determine the strength of the solution accordingly. This will aid your plants in growing to their maximum potential.